1. Field of the Invention
The present invent ion relates to a thermal transfer recording method and apparatus for recording an image onto a recording medium by transferring the ink contained in an ink sheet to the recording medium, and a facsimile terminal equipment using said apparatus, and more particularly to a thermal transfer recording apparatus wherein the length of ink sheet to be used for the recording is L/n (n&gt;1) for a predetermined recording length L of the recording medium.
2. Related Background Art
Generally, a thermal transfer printer uses an ink sheet with the heat-fusible (or heat-sublimable) ink applied to the base film to heat selectively the ink sheet with the thermal head in accordance with an image signal, and record an image by transferring the fused (or sublimated ) ink onto a recording sheet. As this ink sheet in general allows the ink to be transferred entirely onto the recording sheet with one time of recording (a so-called one-time sheet ), it is needed to convey the ink sheet by an amount corresponding to the recorded length and then to bring unused part of the ink sheet to the next recording position with accuracy, after one character or line has been recorded. Therefore, the usage of the ink sheet is increased, the running cost for the thermal transfer printer tends to be greatly higher than for the ordinary thermal sensitizing recording apparatus which records onto a thermosensible sheet.
To solve the above problem, a thermal transfer printer has been proposed in which a recording sheet and an ink sheet are conveyed with a difference of speed, as described in U.S. Pat. No. 3984809, Japanese Laid-Open Patent Application No. 57-83471 or No. 58-201686, or Japanese Patent Publication No. 62-58917.
The present invention has further developed those described in the publications as above mentioned.
As the ink sheet for use in the thermal transfer printer, an ink sheet allowing for the multiple times (n) of image recording (so called a multi-print sheet) is known, with which it is possible to record a recording length L continuously, while the length of conveying the ink sheet after or during image recording is less than the length L (L/n : n&gt;1) . Thereby, the use efficiency of the ink sheet can be increased to n times that for a conventional one, which will lead to a reduced running cost in the thermal transfer printer. Thereinafter, such a recording method is called as the multi-print.
When the multi-print is used with such an ink sheet, it is necessary that the ink sheet is conveyed a fixed distance for a predetermined length of recording.
In such a thermal transfer printer, the ink sheet having a width substantially corresponding to one page of recording sheet is conveyed by winding it. This can be performed by rotating a rotation shaft of a take-up roller for the ink sheet. With such a constitution, a take-up mechanism of the ink sheet is simple, and the ink sheet can be pulled with substantially the same force across the width direction, so that there is the advantage that the recording can be fairly made without yielding any wrinkles on the ink sheet.
In such a conveyance control, if the conveyance amount of the ink sheet is controlled with the rotation of a support shaft of the take-up roll for the ink sheet, the diameter of the take-up roll for taking up the ink sheet is larger with increasing usage of the ink sheet, so that even if the take-up roll is controlled for the same amount of rotation, the conveyance distance of the ink sheet may be different depending on the take-up position. Therefore, the ink sheet may be conveyed by means of a capstan roller and a pinch roller for carrying the ink sheet therebetween.
However, in order to take up the ink sheet, it is necessary to pull the ink sheet with a great force in a take-up direction, so that those rollers may be disordered in a long service time, and can not convey the ink sheet evenly. Further, there is a problem that the mechanical unit becomes complex with the rollers, thereby increasing the cost.
Also, a thermal transfer printer has been proposed in which the conveyance length of the ink sheet is made substantially constant relative to that of the recording sheet in such a way as to detect the rotation amount of an ink sheet supply roller relative to a predetermined driving amount (number of driving steps) for an ink sheet conveying motor, and adjust the rotation amount of an ink sheet conveying motor in accordance with that detected value. However, such thermal transfer printer is constituted in such a way that when the ink sheet is exchanged due to the exhaustion of ink sheet, the adjustment for the rotation amount of the ink sheet conveying motor made with reference to a recorded result of the first page, so that the conveyance length of the ink sheet can not be made constant relative to that of the recording sheet unless the first page has been recorded. Thus, there is a problem that the image quality of recording can not be assured in recording the first page after the ink sheet cartridge is exchanged. Also, there is a problem that if the ink sheet cartridge is exchanged at the power off, the driving of the ink sheet conveying motor after the power on will be made with the rotation amount determined based on the ink sheet cartridge prior to the exchange, which is unsuitable for the ink sheet cartridge after the exchange, so that the conveyance length of the ink sheet can not be made constant.